Fault sensing and driving system for output driver device

Abstract

A driver circuit (10), with a minimum number of interconnects between itself and a conventional output driver device (14), controls the normal on/off operation of the output driver device, and additionally senses various fault conditions within the output driver device. The driver circuit (10) also preferably shuts down the output driver device when the latter device begins to operate in a current limiting mode, and generates diagnostic signals which identify the type of fault condition that is sensed.

What is claimed is: 
     
       1. A fault sensing and driving system for use with an output driver device that has internal current limiting capabilities, a gate-drive terminal, and an output terminal for connection to a load, the system comprising: a logic circuit having an input/output terminal;   coupling means for coupling the logic circuit's input/output terminal to the gate-drive terminal of the output driver device,   the logic circuit including drive control circuitry coupled to the input/output terminal for sending a control signal to the output driver device via said coupling means for turning the output driver device off and on in a normal operating mode,   the logic circuit further including sensing means coupled to the input/output terminal and to the output driver device via said coupling means for sensing a current limiting condition in the output driver device, the sensing means also being coupled to the logic circuit's drive control circuitry for causing the drive control circuitry to turn off the output driver device when a current limiting condition is sensed,   whereby the logic circuit can, using only one of its terminals and one terminal on the output driver device, control the normal operation of the output driver device, sense a current limiting condition in the output driver device, and shut the output driver device down during current limiting to reduce power consumption.   
     
     
       2. A system as set forth in claim 1 wherein the logic circuit further includes a fault signalling circuit, responsive to the sensing means, for generating a signal that is indicative of the current limiting condition. 
     
     
       3. A system as set forth in claim 1 wherein the sensing means includes: means generating a first reference signal;   a comparator receiving the first reference signal and being coupled to the input/output terminal for receiving a fault signal indicative of current limiting in the output driver device, and for comparing the fault signal to the first reference signal.   
     
     
       4. A system as set forth in claim 3 wherein the drive control circuitry includes an impedance coupled to the input/output terminal such that, when a current limiting condition occurs in the output driver device, a voltage drop occurs across the impedance for lowering the signal level at the input/output terminal, which lowered signal level constitutes the fault signal received by the comparator for generating an indication of the current limiting condition. 
     
     
       5. A system as set forth in claim 1 wherein the logic circuit includes a load sensing terminal, wherein the load sensing terminal is coupled to the output terminal of the output driver device, and wherein the logic circuit includes additional sensing means coupled to the load sensing terminal for sensing the presence of a fault condition in the output driver device. 
     
     
       6. A system as set forth in claim 5 wherein the logic circuit includes a fault signalling circuit responsive to the sensing means and to the additional sensing means for generating a signal that is indicative of the type of fault condition that is sensed. 
     
     
       7. A system as set forth in claim 6 wherein the additional sensing means includes: a voltage source coupled to the load sense terminal so as to impose a reference voltage on the input/output terminal when the load is decoupled from the output terminal of the output driver device; and   a comparator coupled to the load sense terminal for comparing the voltage at said load sense terminal to a predetermined reference level.   
     
     
       8. A system as set forth in claim 7 wherein the additional sensing means also includes: a second comparator coupled to the load sense terminal for comparing the voltage at said terminal to a further predetermined reference level for sensing when the output terminal is shorted to ground.   
     
     
       9. A driver circuit for use with an output driver device that has internal current limiting capabilities, a gate-drive terminal, and an output terminal for connection to a load, the driver circuit comprising: an input/output terminal for connection to the gate-drive terminal of the output driver device;   a load-sensing terminal for connection to the output terminal of the output driver device;   drive control circuitry coupled to the input/output terminal for sending a control signal to the output driver device via said input/output terminal for turning the output driver device off and on in a normal operating mode;   first sensing means coupled to the input/output terminal for sensing a current limiting condition in the output driver device via the input/output terminal, the first sensing means also being coupled to the drive control circuitry for causing the drive control circuitry to turn off the output driver device when a current limiting condition is sensed;   additional sensing means coupled to the load sensing terminal for sensing the presence of a fault condition in the output driver device; and   a fault signalling circuit, responsive to the first sensing means and to the additional sensing means, for generating a signal that is indicative of a sensed condition.   
     
     
       10. A driver circuit as set forth in claim 9 wherein the additional sensing means includes: means for developing, at the load-sensing terminal, a fault signal that differs from a predetermined reference value in response to an open condition in the load, and that differs from a different predetermined reference value in response to the output terminal being shorted to ground; and   means for sensing differences between the fault signal and the predetermined reference values.